Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, the submersible pumping system includes a number of components, including one or more fluid filled electric motors coupled to one or more high performance pumps. Each of the components and sub-components in a submersible pumping system must be engineered to withstand the inhospitable downhole environment, which includes wide ranges of temperature, pressure and corrosive well fluids.
Components commonly referred to as “seal sections” protect the electric motors and are typically positioned between the motor and the pump. In this position, the seal section provides several functions, including transmitting torque between the motor and pump, restricting the flow of wellbore fluids into the motor, protecting the motor from axial thrust imparted by the pump, and accommodating the expansion and contraction of motor lubricant as the motor moves through thermal cycles during operation. Many seal sections employ seal bags to accommodate the volumetric changes and movement of fluid in the seal section.
As the use of downhole pumping systems extends to new applications, traditional seal bags may not be suitable. For example, the use of downhole pumping systems in combination with steam assisted gravity drainage (SAGD) technology exposes seal bag components to temperature in excess of 500° F. Of particular concern is the potential for liquid water permeation through the seal bags at these extreme temperatures. In particular, water ingress into the electric motor can affect the preferred properties of the motor, such as favorable lubrication, dielectric and chemical compatibility. To increase the resistance of the seal bag to degradation under these increasingly hostile environments, manufacturers have employed durable polymers, including various forms of polytetrafluoroethylene (PTFE), as the preferred material of construction. More recently, extruded perfluoroalkoxy (PFA) fluoropolymers tubing has become a material of choice for seal bags. The use of PFA as the material of construction in seal bags is disclosed in U.S. Pat. No. 8,246,326 issued Aug. 21, 2012 and assigned to GE Oil & Gas ESP, Inc.
Although generally effective, PFA and many other elastomeric and polymeric materials are nonetheless susceptible to water ingress due to transmission by permeation or diffusion through the material at extremely high temperatures. There is, therefore, a need for a method of further reducing the permeability of the seal bag, seal sections and submersible pumping systems. It is to this and other needs that the present invention is directed.